WEDNESDAY, March 27 (HealthDay News) -- Gastric bypass surgery may help people lose weight by changing the makeup of bacteria living in the intestines, suggests a new study conducted in mice.

Scientists from Harvard University and Massachusetts General Hospital in Boston discovered that performing gastric bypass surgery on mice altered the composition of the bacterial colony living in the animals' guts. Even when they did not perform the surgery, and just transferred the new bacterial colony into the intestines of mice, those mice lost weight.

"Simply by colonizing mice with the altered microbial community, the mice were able to maintain a lower body fat, and lose weight -- about 20 percent as much as they would if they underwent surgery," senior study author Peter Turnbaugh, a Bauer Fellow at Harvard's Faculty of Arts and Sciences Center for Systems Biology, said in a statement.

Turnbaugh's research partner said the implications of the finding might one day be far-reaching.

"Our study suggests that the specific effects of gastric bypass on the microbiota contribute to its ability to cause weight loss, and that finding ways to manipulate microbial populations to mimic those effects could become a valuable new tool to address obesity," senior study author Lee Kaplan, director of the Obesity, Metabolism and Nutrition Institute at Massachusetts General, said in a statement.

"The ability to achieve even some of these effects without surgery would give us an entirely new way to treat the critical problem of obesity, one that could help patients unable or unwilling to have surgery," Kaplan added.

Another expert agreed that the gut is intricately tied to weight loss.

"The gut is a key player in metabolism, and this makes it even more than ever an ideal target for interventions for treating metabolic diseases and obesity," said Dr. Francesco Rubino, a researcher and metabolic surgeon with the Catholic University of Rome, in Italy.

It may someday be possible to use medication or changes in diet to help people lose weight by changing the makeup of germs in the intestine, he said. "We might be doing that with other methods once we understand how the bypass does it."

At issue are the millions, if not trillions, of germs that live in your digestive system, Rubino said.

"For many years, we thought they were a contaminant because we get them from the environment as we eat," he said. But, scientists now understand that the bacteria play a role in the way the body processes food. "We eat for us, but we also eat for them [bacteria]," he explained.

Scientists have suspected that gastric bypass procedures, which funnel food away from the stomach, change the makeup of bacteria in the gut, he said.

Why might gastric bypass have this effect? It appears to be more than simply a matter of the intestinal germs changing because a mouse is eating less, Rubino said. The bypass, by shortening the digestive tract, may actually change "the chemistry of the intestinal environment where these bugs live."

Scientists note that research with animals often fails to provide similar results in humans.

Jeffrey Cirillo, a professor with the department of microbial and molecular pathogenesis at Texas A&M Health Science Center, praised the study but pointed out that one part -- the transfer of germs from one mouse to another -- will be a challenge in humans.

"The transfers were done to germ-free animals, but humans are not germ-free, and it will be difficult to take a pill and get germs to the right location [in the digestive system]," Cirillo said.

The study appears in the March 27 issue of Science Translational Medicine.